The present invention relates to a new and improved construction of radiation detector for the simultaneous detection of electromagnetic radiation emanating from a number of separate receiving regions with the aid of a single radiation receiver.
Such detectors serve, for instance, for detecting objects or persons in a supervised room or area, for instance for the purpose of protecting against unauthorized entry or thievery.
It is already known to the art to detect electromagnetic radiation, for instance light, infrared- or ultraviolet-radiation emanating from a number of different receiving directions by employing a number of separate radiation detectors having directional characteristic. The receiving direction of the individual radiation detectors is adjusted to the desired radiation receiving directions. Such technique is, however, extremely complicated and expensive to carry out and the adjustment to the desired receiving directions is exceptionally difficult.
Therefore, attempts have repeatedly been made to construct a radiation detector, for receiving radiation from a number of different directions, having only a single radiation receiver. According to a prior art radiation detector of this type a screen equipped with a number of openings is mounted at a certain spacing from the single radiation receiver. The radiation can enter through the openings and impinge upon the radiation receiver. The connection lines between the radiation receiver and the individual openings correspond to the different provided radiation receiving directions. With such arrangement the individual receiving regions, however, possess a relatively large aperture angle, which furthermore cannot be adjusted. An exact adjustment to certain points or sectors is therefore not possible with this state-of-the-art arrangement.
Further, it is known for instance from U.S. Pat. No. 3,703,718 to produce different discrete receiving directions by means of optical bundling means, such as with the aid of a number of spherical lenses or spherical mirror-sections, the optical axes of which are aligned in accordance with the desired receiving directions, and a common radiation receiver is arranged at their focal points. What is disadvantageous with this proposal is that the shape and extent of the receiving region cannot be randomly selected and accommodated to given conditions. In the case of larger receiving regions it is necessary to provide a multiplicity of reflectors, rendering the installation impermissibly complicated and expensive.